title: Effect of a patent foramen ovale on pulmonary gas exchange efficiency at rest and during exercise.
abstract: The prevalence of a patent foramen ovale (PFO) is ~30%, and this source of right-to-left shunt could result in greater pulmonary gas exchange impairment at rest and during exercise. The aim of this work was to determine if individuals with an asymptomatic PFO (PFO+) have greater pulmonary gas exchange inefficiency at rest and during exercise than subjects without a PFO (PFO-). Separated by 1 h of rest, 8 PFO+ and 8 PFO- subjects performed two incremental cycle ergometer exercise tests to voluntary exhaustion while breathing either room air or hypoxic gas [fraction of inspired O(2) (FI(O(2))) = 0.12]. Using echocardiography, we detected small, intermittent boluses of saline contrast bubbles entering directly into the left atrium within 3 heart beats at rest and during both exercise conditions in PFO+. These findings suggest a qualitatively small intracardiac shunt at rest and during exercise in PFO+. The alveolar-to-arterial oxygen difference (AaDo(2)) was significantly (P < 0.05) different between PFO+ and PFO- in normoxia (5.9 ± 5.1 vs. 0.5 ± 3.5 mmHg) and hypoxia (10.1 ± 5.9 vs. 4.1 ± 3.1 mmHg) at rest, but not during exercise. However, arterial oxygen saturation was significantly different between PFO+ and PFO- at peak exercise in normoxia (94.3 ± 0.9 vs. 95.8 ± 1.0%) as a result of a significant difference in esophageal temperature (38.4 ± 0.3 vs. 38.0 ± 0.3°C). An asymptomatic PFO contributes to pulmonary gas exchange inefficiency at rest but not during exercise in healthy humans and therefore does not explain intersubject variability in the AaDO(2) at maximal exercise.
authors.affiliation: University of Oregon, Department of Human Physiology, Eugene, Oregon, USA.
authors.forename: Andrew T
authors.initials: AT
authors.lastname: Lovering
authors.forename: Michael K
authors.initials: MK
authors.lastname: Stickland
authors.forename: Markus
authors.initials: M
authors.lastname: Amann
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: O'Brien
authors.forename: John S
authors.initials: JS
authors.lastname: Hokanson
authors.forename: Marlowe W
authors.initials: MW
authors.lastname: Eldridge
mesh_terms: D054092:Foramen Ovale, Patent / Q000503:physiopathology*; D006801:Humans; D008875:Middle Aged; D010807:Physical Endurance; D005082:Physical Exertion; D011659:Pulmonary Gas Exchange; D012146:Rest; D055815:Young Adult